Modern telephone systems increasingly offer a data communication capability. Typically, this data capability is provided by dedicating a separate system port for each connection of a modem or a data set, thereby reducing the number of system ports available for voice communications.
One prior communication system enables the user to connect a modem through a station set and substitute data communication for voice communications thereat. In that system each station set is connected to a control module over a two pair communication facility in which dialed voice or data connections can only be made over one pair, the other pair being used for receive only voice communications or for two-way voice communications if a voice adjunct is connected to a port of the station set. When a data call, over a modem connected to the station set port, is made over the first pair, it prevents the station set from establishing a concurrent voice call over the second pair. What is desired is a method and apparatus for enabling station sets to concurrently establish both a data call and a voice call.